Preliminary work from several laboratories including our own seems to indicate that differences between DNA polymerases (DP's) from normal and malignant human cells may indeed occur. Thus we propose to examine polynucleotides (such as thiolated polynucleotides, polymers of cytokinins and others) and semi-synthetic derivatives (which appear to be more potent than the parent compounds) of various streptovaricins to (a) serve as probes to reveal differences between purified DP's (prepared according to the chromatographic and gradient fractionation procedures already worked out) from normal and leukemic human cells and to substantiate any differences which may be noted by other means including chromatographic behavior, template/primer requirements, reaction requirements, stability, infidelity of deoxynucleotide incorporation etc. (b) To find selective inhibitors of leukemic cell DP's (cellular or viral in origin) so that such inhibitors may be useful in the chemotherapy of leukemia because of their selective cytotoxicity against leukemic cells or by prevention of "re-infection", if relapse in leukemia involves "re-infection" by a putative oncorna virus.